There a few different ways to do a bilingual site. I've done a few
Spanish/English sites for clients of mine, I've used a few of the ways. But
most of them require a dynamic database driven site and web programming (i.e.
asp.net) which is beyond the scope of Publisher which is designed for small
static sites.
But basically I put a simple textual link at the top right corner of the
page. If you're on the English version the link says Espanol, the Spanish
version says Ingles.
The link toggles between the two.
In your situation if you are creating a larger site I'd recommend using
multiple pub files which DF has mentioned already. If you're not and having a
somewhat bigger web publication file is fine then just keep it simple and
make two copies of each page in the pub file. Design the English page, then
do an Insert page using copy all objects from page, so you create the
duplicate. Go thru that one and translate the content. Then add a link to it
that points to the English one. Go back to the English one and add a link to
it that points to the translated one. Then repeat. Basically every other page
in your pub file would be English. Now creating the publication in a English
page, French Page, English page, etc. will be easier to keep track of but you
don't have too. Any page in the publication can link to any page in the
publication.